In message-based operating systems, the calling or invocation of programmatic procedures of the operating system involves a messaging system. The invocations of programmatic procedures of the operating system result in corresponding messages being passed through the messaging system from a sender process to a receiver channel, and ultimately to a receiver process.
In some systems, access control governs the ability of a subject to perform operations on objects. Mandatory access control governs access to the objects independent of ownership of the objects. In contrast, discretionary access control controls govern access to the objects based on the subject's ownership of the object.